JSDoc Type cast to `const` does not work in variable-like initializers

[rbuckton]

Bug Report

🔎 Search Terms

jsdoc cast as const

🕗 Version & Regression Information

• We have half-supported as const in JSDoc since it was added to TypeScript (~v3.5)

⏯ Playground Link

Playground link with relevant code

💻 Code

// @checkJs: true
// @allowJs: true
// @strict: true

let x = /** @type {const} */(1); // error: cannot find name 'const'
x; // any

let y;
y = /** @type {const} */(1); // works
y; // 1

let z = (/** @type {const} */(1)); works
z; // 1

🙁 Actual behavior

In a JavaScript file, using a /** @type {const} */( expr ) cast in the initializer of any variable-like declaration reports a "Cannot find name 'const'" error:

• VariableDeclaration
• PropertyDeclaration
• PropertyAssignment
• BindingElement
• ParameterDeclaration

In any other position, the cast correctly behaves like a TypeScript as const assertion.

🙂 Expected behavior

In a JavaScript file, using a /** @type {const} */( expr ) cast should behave like TypeScript's as const in any position, not just random arguments.

Workaround:

While let x = /** @type {const} */({a: 1}) does not work, let x = (/** @type {const} */({a: 1})) does. This is because our logic to get the effective type annotation node for a variable-like declaration treats the type cast in the initializer as part of the declaration.